Analysis of cases of 3-methylcrotonyl CoA carboxylase deficiency (3-MCCD) in the California newborn screening program reported in the state database.

•We queried the CA state database on all cases of 3-MCCD diagnosed from 2005 to 2010.•The availability of diagnostic data varied significantly between subjects.•A portion of the 3-MCCD “confirmed” cases have a mild biochemical phenotype.•The clinical significance of these mild biochemical cases is unknown.•Further studies are necessary to validate the data and characterize this cohort.